The present invention relates to a tool-magazine indexing device for rapidly indexing tools by the utilization of pressure oil.
In machine tools fitted with tool exchange means, a tool indicated by a numerically controlled device is taken out from a tool-magazine and affixed to a main shaft by means of a tool exchange arm. In general, the tool-magazine is provided with tool-holding portions arranged at equal intervals on a disc or tool-holding members attached to a chain of definite pitch, and such a mechanism is combined with the tool-magazine as is capable of indexing and stopping the indicated tool in a tool exchange position by driving and rotating the disc or chain. The aforesaid tool-holding portions are provided with individual numbers which correspond to the tools housed in the tool-magazine. When one of the members is called by the numerically controlled device, a signal corresponding to said number is transmitted through the combination of each tool-holding portion and a corresponding limit switch dog fixed on the disc. When this signal coincides with the aforesaid called number from the numerically controlled device, the rotary driving of the disc or chain will stop and then the indexing of a tool becomes possible. Even in this case, however, it is impossible to stop the disc or chain immediately upon coincidence of the called number and the signal of the limit switch dog so that, in common practice, the rotary driving speed of the disc or chain must be reduced beforehand and a stop signal is transmitted just when the called number has coincided with the signal of the limit switch dog, thereby stopping the disc or chain in a permissible position. Due to this kind of mechanism, it has heretofore been customary to require that provision of a speed-reducing limit switch before an indexing position so as to transmit a speed-reducing signal.
In case the disc or chain is stopped in a specified position and another tool number is to be called, one set of speed-reducing limit switches is sufficient insofar as the direction of rotation of the disc or chain is always constant, but since no nearest possible rotation is allowed in such a case, it becomes necessary to drive the disc or chain for almost one circumferential rotation, thus requiring too much time of number calling and also waiting time. Moreover, in cases where a tool-magazine is attached to the main body of the machine tool, the driven vibrations of the disc or chain will be transmitted to a workpiece during a machining operation until its precisioned machining becomes impossible. In order to prevent such bad influence, the machining of the workpiece must be suspended halfway with the result of lowering the percentage of working efficiency. In the case of attempting to lessen the time of tool exchange by driving the disc or chain for the nearest possible circumferential rotation, it becomes necessary to provide two sets of speed-reducing limit switches at both sides of an indexing position and, in addition, a mechanism for determining the nearest possible rotation must be provided so that all the device becomes complicated in structure and at the same time, a considerable increase in cost cannot be avoided.